The present invention relates to cameras designed to be mounted on an airborne platform to provide recordable high-resolution images of a scene in the form of a strip that is elongate in the travel direction of the platform.
A particularly important application of the invention lies in the field of devices for air reconnaissance at a safe distance and placed on an airborne platform (generally an aircraft) whose motion causes the scene to be scanned in the travel direction of the platform. The speed of the platform determines the apparent speed of the scene and the rate at which images must be taken in order to ensure that successive images overlap in the travel direction.
In many cases, the resulting images must be of high resolution, compatible with the smallest size of object to be identified. When it is desirable to have an image that can be used immediately, which excludes the use of a photographic camera, the most appropriate detector is a camera having a matrix of sensors, generally charge-coupled sensors, that provide high resolution in the focal plane. In spite of such high resolution, the identification of objects at a safe distance (generally more than 15 km), and seen at an oblique angle, requires the field to be reduced to a very small size by using an optical system of long focal length. Consequently, the apparent speed of the image is too fast for said image to be reproduced on a monitor enabling the pilot of the aircraft to perform surveillance in the scanned strip. In practice, a full screen goes past in less than one second.
Numerous types of high-resolution long-range camera have been proposed. However known solutions suffer from one or more defects: they require the detector to be gyroscopically stabilized in order to conserve coherence between successive images in the travel direction suitable for enabling them to be connected one to another in spite of the pitching motion of the platform, and above all its rolling and yawing motion; they exclude any possibility of being associated with the display tools and detectors already commonly used on board reconnaissance aircraft; they have insufficient sensitivity at low light levels; and they do not enable the pilot to supervise the acquisition of images because of the apparant speed being too fast.